The present invention relates to a torsion element made of a torsionally soft, flexurally stiff torsion rod having piezoceramic fibers wound thereon and of electrodes electrically contacting the piezoceramic fibers, and to a torsional actuator formed thereby.
In the actuator technology, there is frequently a need for actuating elements which are able to execute rapidly oscillating rotary motions in the medium and higher angular range. Thus, for example, to improve the aerodynamic conditions of profiles, such as rotor blades, with respect to oncoming flow, it is desired to move flaps with high actuation frequency using such torsional actuators.
A way to accomplish this is to make use of structural or material-related anisotropies by converting a longitudinal force on the upper or lower side of the rotor blade into a torsional motion of the rotor blade. In this context, the rotor blade is designed to be active itself; however, it must also be designed in such a manner that it is capable of supporting the prevailing wind loads. Another possibility is to integrate a torsional actuator into the rotor blade. In this case, the torsional actuator assumes the adjusting force and serves at the same time to take up the wind loads while the remaining structure of the rotor blade is relieved of this function.
In this context, a torsional actuator includes an active torsion element which generates the force and the actuating action when applying an electric voltage. Using further components of the torsional actuator, this actuating action is converted into an actuating force which is suitable for the respective application, including the required actuating angle, torque and frequency.
A torsion element having piezoceramic fibers wound on a torsion rod is known from German Patent DE 40 33 089 C1. In this context, in order to effect a twisting action on the torsion rod, the piezoceramic fibers are wound on the torsion rod at an angle, to be more precise, at an angle not equal to 90° with respect to the longitudinal axis of the torsion rod. A composite wrap in a 90° direction (directly transverse to the rod) would, after driving the piezoceramic fibers, produce a contraction thereof, and thus a compression of the diameter of the torsion rod, but not a torsion. This would only affect the damping behavior of the rod. The torsional power (torque) and the direction of torsion can be adjusted via the winding density of the piezoceramic fibers and the angle (pitch) between the winding direction and the longitudinal axis of the torsion rod.
In German patent DE 40 33 089 C1, the contacting of the piezoceramic fibers is implemented such that the fibers have an electrically conductive core and are embedded in an electrically conductive matrix so that the electrodes are run virtually parallel to the piezoceramic fiber. For control purposes, the respective core of each fiber must be directly contacted in order to apply a voltage between this core and the matrix.
However, in the manufacture of such a torsion element, this is extremely difficult in terms of process engineering so that often several fibers are not driven or fail during operation, resulting in a deterioration of the functioning of the torsion element.